Error 20 is caused because root is installed (Timestamp changed)
- Open Magisk
- Click on
Uninstall Magisk
>RESTORE IMAGES
- Reboot
- Search & install the Update from
Options
>About phone
>Software info
>NOTHING OS (1)
>Check for update
https://github.com/K3V1991/How-to-flash-Android-Kernel-and-Recovery
- Download the Full Version of the Firmware you installed
- Create a Folder named "ota" in the Root of Phone
- Put the Update Zip in the created Folder
- Open the Dialer and type:
*#*#682#*#*
- Local System Update opens, select the Update Zip
- Tap
PROCEED & REBOOT
- The Phone reboot, first Initialisation after Update
- Reboot to Bootloader
- Boot a Magisk Patched Boot Image by using the Command:
fastboot boot <kernel file name>.img
- Phone reboots to System
- Open Magisk
- Tap the
Install
Button - Choose
Direct Install (Recommanded)
- Reboot (If the Magisk patched Boot File don't boot, just do a hard Shutdown by pressing ON/OFF Button for 5 Seconds, the Device reboots with your Stock Boot)